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While loop syntax:
while (some_expression) {
statment_1;
statment_2;
....
}
When the program executes the statement while, first check the control statements (some_expression), if it is true, the loop body will be executed once, so repeated constantly perform, know the control statement is false, then stop while cycling
Example:
#! / Usr / bin / perl -w
$ Number = 10;
while ($ number> 0) {
print ( "number is $ number \ n");
- $ Number;
}
until loop syntax
until (some_expression) {
statment_1;
statment_2;
...
}
And while statements contrary, some_expression false the loop body is executed, that is true stop the loop
Example:
#! / Usr / bin / perl -w
$ Number = 10;
until ($ number < = 0) {
print ( "number is $ number \ n");
- $ Number;
}
do while loop and do until loop syntax
do while or do until loop the loop executed at least once before the condition is checked.
do {
statment_1;
statment_2;
...
} While (some_expression);
do while loop, the conditional expression is false then the loop ends
do {
statment_1;
statment_2;
...
} Until (some_expression);
do until loop, the conditional expression is true then the end of the loop
for loop
for statement is mainly used to determine the number of cycles, the syntax is as follows:
for (in fact statement; test statement; stepping statement) {
statment_1;
statment_2;
....
}
First, the system will perform the initial statement. Usually you can assign values to variables here, but this is not mandatory, or even nothing to write, but to write or semicolon. If the value of the test the statement is true, the loop is executed once, then execute step statement.
foreach loop
foreach loop can receive a list, which will be assigned to a primary data as a parameter of a scalar variable, and the implementation of an effective assignment of each block of code statements. Its syntax is as follows:
foreach $ i (@some_list) {
statment_1;
statment_2;
....
}
Example:
#! / Usr / bin / perl -w
foreach (1..10) {
print "";
print;
}
print "\ n";
Leaping list any statement foreach list is used, not necessarily the array variable, you can not even write a scalar variable, so perl using the default variable $ _. If you do not specify any value to print, it will print out the contents of $ _.
If the list of values should be used where the use of a real variable, the function returns a list of substitution, then perl will be used in a loop to pass variables as aliases variables, rather than just copy values only. Thus, if you change the scalar variable in a loop, the corresponding element in the list will be changed accordingly. E.g:
#! / Usr / bin / perl -w
@ X = (1..10);
foreach $ num (@x) {
$ Num + = 10;
}
print "@x";
print "\ n";
foreach after the implementation, the value of the array @x changed. |
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